Mechanistic Studies of Formate Oxidation on Platinum in Alkaline Medium

The electro-oxidation of formate (HCOO – ) on polycrystalline Pt in highly basic medium (pH = 14) has been investigated by cyclic voltammetry, differential electrochemical mass spectrometry, potential step-linear sweep voltammetry, and adsorbate stripping experiments. Low oxidation currents were observed for HCOO – oxidation indicating that HCOO – is only weakly active under these conditions. The activity of HCOO – is confined to low potentials (0.2 V < E < 0.7 V vs RHE). Our results suggest a dual pathway mechanism for HCOO – oxidation, analogous to HCOOH oxidation in acid. In the case of HCOO – oxidation, the direct and indirect pathway analogues are referred to as the primary and secondary pathways, respectively. Formation of CO ads from HCOO – was observed to be slow. We also find that oxidation of CO ads (the secondary pathway) is strongly coupled to the oxidation of HCOO – through the primary pathway. Moreover, the oxidation of CO ads did not appreciably enhance HCOO – oxidation through the primary pathway, signifying the presence of other inhibitory processes such as OH adsorption. Adsorbate stripping experiments revealed, in addition to CO ads, the presence of a stable adsorbate that can undergo oxidation. We also find that the latter can be converted to CO ads in the H upd region. On the basis of the results obtained, a tentative mechanism of HCOO – oxidation in basic media is proposed.